1. Field of the Invention
The present invention relates to an aircraft separator system for separating moisture from air in an aircraft waste system. More particularly, the present invention relates to a disposable separator sized large enough to decrease air velocity and optimize moisture separation from the air, but small enough to fit within limited aircraft space, located externally to a waste tank to reduce exposure to waste and facilitate service, with a dual-stage, dual-density filter/demister to separate the moisture from the gas, and with a deflector shield to minimize passage of solids and liquids into the separator.
2. Prior Art
The waste system of an aircraft uses a pressure differential, or vacuum, to move waste from toilets to a waste tank. The air, waste, and water move from the toilets to the waste tail where the air is passed from the waste tank and vented to the atmosphere. The vacuum is typically created by a blower when the aircraft is on the ground or at low altitudes. At higher altitudes, the vacuum is created by venting the system to the lower pressure atmosphere. It is necessary for the air to be free of moisture and other particles for sanitary and aesthetic reasons, and to satisfy Federal Aviation Administration (FAA). For example, the moisture, called blue ice, may build up on the fuselage, which affects aircraft performance and may fall off causing injury. Two key performance requirements require (1) a specific air flow rate at a maximum pressure drop, and (2) a "flush and overboard" test where the toilets are first repeatedly flushed at close intervals to fill the waste tank, drawn outside the system.
Conventional liquid/air separators have been used to filter moisture and particles out of the air before venting the air to the atmosphere, or before the air reaches the blower. The separators impart a rotational motion to the air and make use of centrifugal force to separate the heavier fluid from the air. The separators also use a demister, a dense, knitted mesh of metal, nylon, or polypropylene, to trap any remaining moisture.
One disadvantage with these separators is that they are often located, at least partially, within the waste tanks themselves. The location of the separators within the tanks robs the tanks of needed capacity for storing waste. In addition, because of the need to frequently clean the separators and replace the demister material, their location within the tank makes the separators difficult to service. Furthermore, the location of the separators within the waste tank leaves some unfortunate maintenance worker the unpleasant job of reaching into the waste tank and handling the demister material. The cost to replace the demister material is high because workers must frequently suit-up in hazardous material suits, and because workers must often be paid hazard pay to perform such a task.
Another disadvantage of some general separators is their large size. Many separators utilize vanes and cylindrical enclosures to impart a rotational flow to the air in order to force moisture from the air. Other separators utilize a tortuous path with numerous turns to prevent particulate from entering the demister material. The structure used to accomplish the rotational flow and tortuous path tends to require additional space. The space available for equipment on the aircraft, however, is limited. Thus, it is desirable for the separators to be as small as possible to preserve valuable space. In addition, the structure of the aircraft itself may force size requirements on the separator. Furthermore, larger separators tend to require larger openings in the waste tank, thus increasing the risk of foreign objects, such as tools, inadvertently falling into the waste tank during replacement or maintenance. In addition, larger tank openings cause unnecessary exposure to the tank contents. Therefore, many separators are unsuitable due to their large size.
Another disadvantage related to size is airflow. As indicated above, performance requirments require a certain air mass and pressure drop. While it is desirable to reduce the size of the separator, maintaining the required mass flow rate as the size of the separator shrinks tends to increase the velocity of the air flow, thus making moisture separation more difficult.
Therefore, it would be advantageous to develop an aircraft separator system capable of separating the moisture from the air, and capable of meeting FAA approval and performance requirements. It also would be advantageous to develop an aircraft separator system capable of being easily and safely maintained and replaced, reducing exposure to waste, and maintaining the capacity of the waste tank. It also would be advantageous to develop an aircraft separator system capable of being installed in the limited spacial requirements of an aircraft, without compromising performance.